It is preferred in the semiconductor and related arts to utilize large wafers for fabrication of integrated circuits and other devices. Large wafers are preferred inasmuch as an increased number of chips can be fabricated from larger workpieces. As the size of the wafers continues to increase as processing techniques are improved, additional processing obstacles are presented.
For example, it is typically preferred to provide a substantially constant temperature across the surface of the wafers being processed because changes in temperature can influence device fabrication. Wafers of increased diameters and surface areas experience increased temperature fluctuations at various locations on the workpiece. In particular, a partial vacuum is typically used to pull small diameter wafers into direct thermal contact with a hot plate. Such processing methods facilitate substrate temperature control because the substrate temperature is closely associated to the temperature of the hot plate. Fabrication of small sub-micron devices upon larger diameter semiconductor wafers or workpieces requires minimal backside contamination. As such, contact of the workpiece with a hot plate is not typically not possible. Such workpieces are processed in conventional operations upon spacers or pins that position the workpiece approximately 0.1 millimeters above the hot plate heating surface. Such spacing intermediate a chuck or hot plate and the workpiece results in substrate temperatures which can be influenced by the environment above the substrate. Inconsistencies in temperature across the surface of the workpiece often result.
Absolute temperature and temperature uniformity of a workpiece are parameters which are closely monitored during wafer and workpiece fabrication to provide critical dimension (CD) control. Chemically amplified resists are utilized in deep ultraviolet (DUV) lithography in small micron geometries (eg., 0.25 microns and below). Chemically amplified resists are particularly temperature dependent further increasing the importance of temperature control and monitoring. Some thermal resist processing steps require process windows ranging from 1–2 degrees centigrade down to a few tenths of a degree centigrade. Meteorology that is four to ten times more precise than conventional process equipment may be required to provide thermal performance measurements to 0.1 degrees centigrade.
One approach has disclosed the use of temperature sensors across a surface of the wafer to provide temperature mapping of the workpiece during processing. Platinum foil leads and copper leads are utilized to electrically connect the temperature sensors. With the use of numerous temperatures sensors across an entire workpiece surface, numerous wires are required for coupling and monitoring. Such numerous wired connections can break and/or adversely impact processing of the workpiece or the temperature measurements taken of the surface of the workpiece. Some temperature sensors require four leads per sensor further impacting the processing and temperature monitoring of the workpieces.
Therefore, there exists a need to provide improved temperature monitoring of workpieces which overcomes the problems experienced in the prior art.